The invention is related to precursors for lithium transition metal oxides for rechargeable batteries, the precursors having a unique characteristic to provide excellent battery materials for demanding technologies such as automotive applications.
Due to their high energy density, rechargeable lithium and lithium-ion batteries can be used in a variety of portable electronics applications, such as cellular phones, laptop computers, digital cameras and video cameras. Commercially available lithium-ion batteries typically consist of graphite-based anode and LiCoO2-based cathode materials. However, LiCoO2-based cathode materials are expensive and typically have a relatively low capacity of approximately 150 mAh/g. Alternatives to LiCoO2-based cathode materials include LNMCO type cathode materials. LNMCO means lithium-nickel-manganese-cobalt-oxides. The composition is LiMeO2—wherein Me stands for metal, but covers also a doped metal—or Li1+x′Me1-x′O2 where Me=NixCoyMnzAm (which is more generally referred to as “NMC”, A being one or more dopants). LNMCO has a similar layered crystal structure as LiCoO2 (space group R-3m). The advantage of LNMCO cathodes is the much lower raw material price of the composition M versus pure Co. The addition of Ni gives an increase in discharge capacity, but is limited by a decreasing thermal stability with increasing Ni content. In order to compensate for this problem, Mn is added as a structural stabilizing element, but at the same time some capacity is lost.
The target lithium-containing composite oxide is generally synthesized by mixing a nickel-cobalt-manganese composite hydroxide as precursor material (having the same metal composition as the final cathode material will have) with a lithium compound and firing the mixture. The cell characteristics can be improved by substituting a part of nickel, cobalt and manganese by other metal elements, such as Al, Mg, Zr, Ti, Sn and Fe. The suitable substituting quantity is 0.1 to 10% of the total quantity of the nickel, cobalt and manganese atoms.
Generally, for the production of cathode materials with complex compositions, special precursors such as mixed transition metal hydroxides NixCoyMnz(OH)2 are used. The reason is that high performance Li-M-O2 needs well mixed transition metal cations. To achieve this without “over sintering”—high temperature sintering for a longer period together with a lithium precursor, typically Li2CO3 or LiOH—the cathode precursors need to contain the transition metal in a well-mixed form—at atomic level—as provided in mixed transition metal hydroxides. Mixed hydroxides with suitable size and morphology are typically achieved by precipitation reactions with the following steps: (1) mixed hydroxides are precipitated in a reactor with a flow of NaOH and a flow of mixed metal salt under controlled pH, (2) the precursor suspension is removed and filtered, (3) the filtered wet cake is dried under defined conditions.
In U.S. Pat. No. 8,980,475 a process for preparing lithium mixed metal oxides is disclosed, which comprises the steps of:
a) the preparation of a mixture designated as intermediate (B) which comprises essentially lithium-comprising mixed metal hydroxides and lithium-comprising mixed metal oxide hydroxides,
                where manganese, cobalt and nickel are comprised in the ratio (1-a-b):a:b and the oxidation state averaged over all ions of manganese, cobalt and nickel is at least 4-1.75a-1.75b, where 0≤a≤0.5 and 0.1≤b≤0.8,        by a thermal treatment carried out with continual mixing and in the presence of oxygen of a mixture (A) comprising at least one transition metal compound and at least one lithium salt (L), during which L does not melt, andb) the thermal treatment carried out without mixing and in the presence of oxygen of the intermediate (B).        
U.S. Pat. No. 8,394,299 discloses a transition metal precursor comprising a composite transition metal compound represented by M(OH1-x)2, as transition metal precursor used in the preparation of a lithium-transition metal composite oxide, wherein M is two or more selected from the group consisting of Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr and the transition metals of 2 period in the Periodic Table of the Elements; and 0<x<0.5.
In U.S. Pat. No. 7,384,706 a method for manufacturing a lithium-nickel-cobalt-manganese-containing composite oxide LipNixMn1-x-yCoyO2-qFq (where 0.98≤p≤1.07, 0.3≤x≤0.5, 0.1≤y≤0.38, and is disclosed, comprising: a step for synthesizing coagulated particles of a nickel-cobalt-manganese composite hydroxide wherein primary particles obtained by precipitating the nickel-cobalt-manganese composite hydroxide are coagulated to form secondary particles, by supplying an aqueous solution of a nickel-cobalt-manganese salt, an aqueous solution of an alkali-metal hydroxide and an ammonium-ion donor continuously or intermittently to a reaction system; a step for synthesizing coagulated particles of a nickel-cobalt-manganese composite oxyhydroxide by making an oxidant act on said coagulated composite hydroxide particles; and a step for dry-blending at least said coagulated composite oxyhydroxide particles and a lithium salt, and firing the mixture in an oxygen-containing atmosphere.
US2009/0302267 discloses a precursor NibM1cM2c(O)x(OH)y, wherein M1 denotes at least one element from the group consisting of Fe, Co, Mg, Zn, Cu and/or mixtures thereof, M2 denotes at least one element from the group consisting of Mn, Al, B, Ca, Cr and/or mixtures thereof, wherein b≤0:8, c≤0.5, d≤0.5 and x is a number between 0.1 and 0.8, y is a number between 1.2 and 1.9, and x+y=2.
U.S. Pat. No. 7,585,432 discloses a process for the production of high density cobalt-manganese coprecipitated nickel hydroxide (Ni(1-x-y)CoxMny)(OH)2 particles (wherein 1/10≤x≤⅓ and 1/20≤y≤⅓); the process comprising the steps of: continuously supplying an aqueous solution of a nickel salt which contains a cobalt salt and a manganese salt, a complexing agent, and an alkali metal hydroxide into a reactor either in an inert gas atmosphere or in the presence of a reducing agent; continuously growing crystals of said particles; and continuously removing crystals of said particles from said reactor.
It is expected that in the future the lithium battery market will be increasingly dominated by automotive applications. Automotive applications require very large batteries that are expensive, and must be produced at the lowest possible cost. A significant fraction of the cost comes from the cathodes, i.e. the positive electrodes. Providing these electrodes by a cheap process can help to lower cost and boost market acceptance. The automotive market includes different major applications. Batteries for EV (purely electric vehicles) need to store energy for several hundreds of km of driving range, necessitating that the cells are very large and heavy. Obviously this requires the battery to have a volumetric energy density that is as high as possible. Apart from cell design and anode energy density, the cathode materials in such batteries also need to have a high capacity at a realistic rate. Battery sets for EV applications contain a big amount of NMC cathode material. Catastrophic exothermal reactions of one cell could induce a chain reaction in the battery and hence cause accidents—as has happened in the past. The battery safety needs to be optimized in all its different aspects, and the cathode material is one of it. EV applications normally require a battery to be used for ten years and within this time frame, the battery capacity should remain higher than 80%. During daily use, the battery's direct current resistance (DCR) will increase during cycling.
An important DCR increase means that more and more energy is lost during charging, and less and less power is available during driving. Keeping a low rate of DCR growth is one of the key for cathode material development for EV application.
If the DCR resistance is small, then the charge—discharge cycle is highly efficient; and only a small amount of ohmic heat evolves. To achieve these high power requirements the batteries contain cells with thin electrodes. This allows that (1) Li diffuses over only short distances and (2) current densities (per electrode area) are small, contributing to high power and low DCR resistance. Such high power batteries put severe requirements on the cathode materials: they must be able to sustain very high discharge or charge rates by contributing as little as possible to the overall battery DCR. In the past, it has been a problem to improve the DCR resistance of cathodes, as is discussed in WO2015/132647. Furthermore, it was a problem to limit the increase of DCR during the long term operation of the battery.
The present invention aims to provide improved precursors of lithium transition metal cathode materials for positive electrodes having an intermediate to high Ni content, made by a cheap process, and the cathode materials having a reduced irreversible capacity Qirr upon cycling in the secondary battery.